In physics, lower case lambda is the Greek letter usually assigned to the wavelength. It looks like an upside-down "y".

Lower case nu is the letter assigned to frequency, it looks like a "v" that's leaning to the right.

Lower case Roman c is the speed of light. (about 300 million meters per second).

For any kind of wave (sound, light, whatever) the wavelength times the frequency gives the speed the wave travels at. So if you know any two, you can always get the third with a little arithmetic.

The equation tells us that the frequency of electromagnetic radiation is related to its wavelength by the constant c, or the speed of light.

It's no big deal, really, frequency is just another term for wavelength, they are related to each other, so knowing one immediately gives you the other. So for example, if you are listening to the hundred meter band on your radio, the frequency you are listening to is 3 million cycles per second. The fancy modern term for this is "Three MegaHertz".

100 meters/cycle X 3,000,000 cycles/sec = 300,000,000 meters/sec

Note that the wavelength is given in units of distance per cycle, the frequency in cycles per time, the cycle unit cancels out in the multiplication and the results are in units of distance per time. Distance per time is the unit of velocity.